The invention herein relates to housings for filters. It is of particular pertinence to housings for the filters and associated support plates used in membrane filtration.
Membrane filtration using microporous filters finds many applications in medical research, beverage production and the drug, electronics and chemical industries. This type of filtration utilizes membrane filters generally in the form of flat sheets containing many microscopic but highly uniform flow passages, generally of the order of several micrometers or less. Such filters are normally supported on rigid plates (sometimes referred to herein as "support plates"). The configuration of the support plates is such that when one is stacked upon another the impure fluid can flow between the support plates and across and through the microporous filters. The liquid filtrate discharged from the filter drains out through the other side of the support plates and is collected or discharged as desired. Typical operation of the plates and filters will be described below in more detail.
Because of the small size of the passages in the filter, much of the filtration using membrane filters is conducted under pressure. Consequently, it is necessary to place the plates and filters in a pressure vessel. In the past there have been various designs of pressure vessels, but most have been designed for a single specific configuration and number of plates. Housings have been of a fixed size, and lesser numbers of plates have been accommodated only by using spacer tubes to substitute for the "missing" plates. It has therefore not been possible to use a single housing with different numbers of stack plates without the use of spacers. However, use of spacers causes an undesirable increase in the amount of "dead" volume in the housing. Typical of such fixed size housings is that illustrated in U.S. Pat. No. 3,343,681.
Previous multiple plate devices have been constructed such that the support plates and filters had to be secured in position prior to closing up the devices. These filters, being thus under stress, could not be consistently sterilized by autoclaving because they would often rupture during the heating/cooling cycle. Consequently, the high degree of sterilization needed for many uses could not be consistently attained.